U.S. patent application number 14/625939 was filed with the patent office on 2015-09-03 for fuel injector.
The applicant listed for this patent is DENSO CORPORATION. Invention is credited to Fumiaki ARIKAWA, Fumihiro FUJIKAKE, Yuuta HASHIMOTO, Kazufumi SERIZAWA, Atsushi UTSUNOMIYA.
Application Number | 20150247478 14/625939 |
Document ID | / |
Family ID | 53801476 |
Filed Date | 2015-09-03 |
United States Patent
Application |
20150247478 |
Kind Code |
A1 |
SERIZAWA; Kazufumi ; et
al. |
September 3, 2015 |
FUEL INJECTOR
Abstract
A fuel injector has a cylindrical nozzle body, a nozzle needle,
a pressure chamber and an injection passage. The injection passage
includes a first hole and a second hole. A minimum vertical
distance between an outer periphery of a first nozzle hole outlet
and a contact point relative to an axial center line of the first
hole is defined as a vertical distance R. A minimum axial distance
between the first nozzle hole outlet and the contact point relative
to an axial center line of the first hole is defined as an axial
distance L. An angle between the axial center line of the first
nozzle hole and the outer periphery line of the fuel spray is
defined as an injection angle .theta.. The vertical distance R, the
axial distance L and the injection angle .theta.satisfy a formula:
R/(L.times.tan.theta.)>6.0.
Inventors: |
SERIZAWA; Kazufumi;
(Obu-city, JP) ; UTSUNOMIYA; Atsushi;
(Kitanagoya-city, JP) ; FUJIKAKE; Fumihiro;
(Anjo-city, JP) ; ARIKAWA; Fumiaki; (Okazaki-city,
JP) ; HASHIMOTO; Yuuta; (Nishio-city, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DENSO CORPORATION |
Kariya-city |
|
JP |
|
|
Family ID: |
53801476 |
Appl. No.: |
14/625939 |
Filed: |
February 19, 2015 |
Current U.S.
Class: |
239/584 |
Current CPC
Class: |
F02M 51/061 20130101;
F02M 61/04 20130101; F02M 61/18 20130101; F02M 61/1833 20130101;
F02M 61/1846 20130101 |
International
Class: |
F02M 51/06 20060101
F02M051/06; F02M 61/18 20060101 F02M061/18; F02M 61/04 20060101
F02M061/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2014 |
JP |
2014-38468 |
Claims
1. A fuel injector comprising: a cylindrical nozzle body; a nozzle
needle axially moving in the cylindrical nozzle body; a pressure
chamber defined between the nozzle needle and the cylindrical
nozzle body for receiving a fuel therein; and an injection passage
defined in the nozzle body to fluidly connect the pressure chamber
and a cylinder of an internal combustion engine, wherein the fuel
in the pressure chamber is injected into the cylinder as a fuel
spray, the injection passage has a first hole which is opened to
the pressure chamber and a second hole which is opened to the
cylinder, an inner diameter of the second hole is larger than an
inner diameter of the first hole, an outer periphery line of the
fuel spray agrees with an inner wall of the second hole at a
contact point, a minimum vertical distance between an outer
periphery of a first nozzle hole outlet and the contact point
relative to an axial center line of the first hole is defined as a
vertical distance R, a minimum axial distance between the first
nozzle hole outlet and the contact point relative to an axial
center line of the first hole is defined as an axial distance L, an
angle between the axial center line of the first nozzle hole and
the outer periphery line of the fuel spray is defined as an
injection angle .theta., and the vertical distance R, the axial
distance L and the injection angle .theta. satisfy a formula:
R/(L.times.tan.theta.)>6.0.
2. A fuel injector according to claim 1, wherein a pressure Pr of
the fuel in the pressure chamber satisfies 25
Mpa.ltoreq.Pr.ltoreq.250 MPa.
3. A fuel injector according to claim 1, wherein the cylindrical
nozzle body has a plurality of injection passages, and the second
hole of each injection passage is not fluidly connected to other
second holes.
4. A fuel injector according to claim 1, wherein the first hole has
a nozzle hole inlet and a nozzle hole outlet, and an inner diameter
of the nozzle hole inlet is equal to an inner diameter of the
nozzle hole outlet.
5. A fuel injector according to claim 1, wherein the first hole has
a nozzle hole inlet and a nozzle hole outlet, and an inner diameter
of the nozzle hole inlet is larger than an inner diameter of the
nozzle hole outlet.
6. A fuel injector according to claim 1, wherein the inner wall of
the second hole is formed in parallel with the axial center line of
the first hole.
7. A fuel injector according to claim 1, wherein an axial center
line of the second hole deviates from the axial center line of the
first hole.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based on Japanese Patent Application No.
2014-38468 filed on Feb. 28, 2014, the disclosure of which is
incorporated herein by reference.
TECHNICAL FIELD The present disclosure relates to a fuel injector
that injects a fuel into a cylinder of an internal combustion
engine.
BACKGROUND
[0002] JP2006-510849A (U.S.2006-0226263A1, DE10325289A1,
CN1798920A) discloses a fuel injector, in particular for a direct
injection of fuel into a combustion chamber of an internal
combustion engine. The fuel injector has a valve-closure member
which cooperates with a valve-seat surface formed on a valve-seat
body, to form a sealing seat. The fuel injector includes at least
one spray-discharge orifice provided downstream from the sealing
seat. The spray-discharge orifice has a guide region and an exit
region arranged at its discharge-side end. The exit region widens
in a stepped manner by at least one first step and/or at least in
part continuously beginning with a transition from the guide region
into the exit region. A fuel jet which emerges from the guide
region at the transition and widens essentially uniformly at a jet
angle, passes a discharge-side end of the exit region with a gap
dimension of a gap after a distance. The gap dimension is greater
than zero and a first volume remaining in the exit region between
the fuel jet and the inner walls of the exit region.
[0003] In the conventional fuel injector, when a pressure of a fuel
spray is lower than a specified value, the fuel spray is formed to
suppress a caulking. However, when a pressure of a fuel spray is
higher than the specified value, the fuel spray is attracted to an
inner wall surface of the injector body. The fuel may adhere to the
inner wall surface.
SUMMARY
[0004] It is an object of the present disclosure to provide a fuel
injector capable of suppressing a caulking and an instability of a
fuel spray shape.
[0005] According to the present disclosure, a fuel injector has a
cylindrical nozzle body, a nozzle needle axially moving in the
cylindrical nozzle body, a pressure chamber defined between the
nozzle needle and the cylindrical nozzle body for receiving a fuel
therein, and an injection passage defined in the nozzle body to
fluidly connect the pressure chamber and a cylinder of an internal
combustion engine. The fuel in the pressure chamber is injected
into the cylinder as a fuel spray. The injection passage has a
first hole which is opened to the pressure chamber and a second
hole which is opened to the cylinder. An inner diameter of the
second hole is larger than an inner diameter of the first hole. An
outer periphery line of the fuel spray agrees with an inner wall of
the second hole at a contact point. A minimum vertical distance
between an outer periphery of a first nozzle hole outlet and the
contact point relative to an axial center line of the first hole is
defined as a vertical distance R. A minimum axial distance between
the first nozzle hole outlet and the contact point relative to an
axial center line of the first hole is defined as an axial distance
L. An angle between the axial center line of the first nozzle hole
and the outer periphery line of the fuel spray is defined as an
injection angle .theta.. The vertical distance R, the axial
distance L and the injection angle .theta. satisfy a formula:
R/(L.times.tan.theta.)>6.0.
[0006] According to the present disclosure, a caulking and an
instability of a fuel spray can be suppressed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The above and other objects, features and advantages of the
present disclosure will become more apparent from the following
detailed description made with reference to the accompanying
drawings. In the drawings:
[0008] FIG. 1 is a longitudinal-sectional view showing a fuel
injector according to a first embodiment;
[0009] FIG. 2 is an enlarged sectional view showing a tip end
portion of the fuel injector according to the first embodiment;
[0010] FIG. 3 is an enlarged sectional view schematically showing
an injection passage according to the first embodiment;
[0011] FIG. 4 is a diagram showing experimental results;
[0012] FIG. 5 is a graph showing a correlation between an injection
angle .theta. and a characteristic value X;
[0013] FIG. 6 is an enlarged sectional view schematically showing
an injection passage according to a second embodiment;
[0014] FIG. 7 is an enlarged sectional view schematically showing
an injection passage according to a third embodiment;
[0015] FIG. 8 is an enlarged sectional view schematically showing
an injection passage according to a first modification; and
[0016] FIG. 9 is an enlarged sectional view schematically showing
an injection passage according to a second modification.
DETAILED DESCRIPTION
[0017] Hereafter, embodiments of the present disclosure will be
described hereinafter. In each embodiment, the same parts and the
components are indicated with the same reference numeral and the
same description will not be reiterated.
First Embodiment
[0018] Referring to FIG. 1 to FIG. 4, a fuel injector 1 of the
first embodiment will be explained, hereinafter.
[0019] The fuel injector 1 has a nozzle body 2, a nozzle needle 3,
and a pressure control portion 10. The pressure control portion 10
controls a pressure in a pressure chamber 5 defined between the
nozzle body 2 and the nozzle needle 3, whereby the nozzle needle 3
moves up and down.
[0020] The nozzle body 2 is cylindrically shaped and is made of
ferrous materials. The nozzle body 2 defines a space therein. The
nozzle needle 3 is accommodated in the space. The pressure chamber
5 is defined between the nozzle needle 3 and the nozzle body 2. The
pressure control portion is arranged at a base end of the nozzle
body 2. A sack portion 21 is formed at a tip end of the nozzle body
2. The sack portion 21 has an injection passage 4 which
communicates the pressure chamber 5 and a combustion chamber (not
shown) of an internal combustion engine. The nozzle body 2 has a
seat portion 21 with which the nozzle needle 3 is brought into
contact.
[0021] The nozzle needle 3 is a column which has three recesses 31
on its outer surface. Each of the recesses 31 extends in an axial
direction of the nozzle needle 3. The fuel flows from the bottom
end to the tip end of the nozzle body 2 through the recesses 31.
The nozzle needle 3 has an annular shim 6. A cylinder 11 of the
pressure control portion 10 is provided to the base end of the
nozzle needle 3. A first spring 71 is disposed between the shim 6
and the cylinder in such a manner as to bias the nozzle needle 3
toward its tip end.
[0022] The pressure control portion 10 includes the cylinder 11, an
orifice plate 8 and a second spring 72. The base end of the nozzle
needle 3 and the orifice plate 8 are arranged inside of the
cylinder 11. The orifice plate 8 has an orifice 81. The orifice 81
communicates with a fuel passage extending from a common-rail (not
shown). A fuel quantity passing through the orifice 81 is adjusted
by an electromagnetic valve provided in the fuel passage.
[0023] The second spring 72 is disposed between the orifice plate 8
and the nozzle needle 3. The second spring 72 biases the orifice
plate 8 toward the base end of the nozzle body 2. Moreover, a
control chamber 9 is defined between the cylinder 11, the orifice
plate 8 and the nozzle needle 3. The fuel is introduced into the
control chamber 9 through the orifice 81. The pressure in the
control chamber 9 is controlled by adjusting the fuel quantity by
the electromagnetic valve.
[0024] When the fuel is less introduced into the control chamber 9,
the pressure in the control chamber 9 is decreased. The nozzle
needle 3 receives a fuel pressure in the pressure chamber 5,
whereby the nozzle needle 3 moves apart from the seat portion 21.
Meanwhile, when the fuel flows into the control chamber 9, the
pressure in the control chamber 9 is increased. The nozzle needle 3
receives the fuel pressure in the pressure chamber 5 and the fuel
pressure in the control chamber 9, which are substantially equal to
each other. The nozzle needle 3 receives the biasing force from the
first spring 71 and the second spring 72, so that the nozzle needle
3 is brought into contact with the seat portion 21. As above, an
axial position of the nozzle needle 3 is controlled by the pressure
control portion 10. According to the position of the nozzle needle
3, the pressure chamber 5 and the injection passage 4 are fluidly
connected or disconnected with each other.
[0025] The pressure chamber 5 is formed between the nozzle body 2
and the nozzle needle 3. The pressure chamber 5 communicates with
an interior of the sack portion 21. The fuel flows into the
pressure chamber 5 from the fuel-passage-inlet 51. The
fuel-passage-inlet 51 is fluidly connected with the common-rail
(not shown). The supplied fuel flows from the fuel-passage-inlet 51
toward the pressure chamber 5 through the recesses 31. When the
nozzle needle 3 moves apart from the seat portion 21, the fuel
flows into the interior of the sack portion 21. Then, the fuel is
injected into the combustion chamber through the injection passage
4.
[0026] Referring to FIGS. 2 and 3, the configuration of the
injection passage 4 will be described in detail. FIG. 3 is a
schematic chart explaining the injection passage 4. The nozzle body
2 has a plurality of injection passages 4 at its tip end. The
injection passages 4 are arranged at regular intervals around a
center line of the nozzle body 2. Thus, the fuel in the sack
portion 21 can be injected into the combustion chamber uniformly.
Each of the injection passages 4 is formed independently mutually.
That is, each injection passage 4 does not interfere with other
injection passages 4.
[0027] The injection passage 4 is configured by a counterbore 42
and a nozzle hole 41. The counterbore 42 is a circular concaved
portion formed on the outer surface of the sack portion 21. A
diameter of the counterbore 42 is larger than that of the nozzle
hole 41. Thus, a stepped surface is formed in the injection passage
4 between the counterbore 42 and the nozzle hole 41. One end of the
nozzle hole 41 is opened to the interior of the sack portion 21 and
the other end of the nozzle hole 41 is opened to the counterbore
42. The counterbore 42 and the interior of the sack portion 21 are
fluidly connected with each other through the nozzle hole 41. The
nozzle hole 41 has a circular cross section. Moreover, an axial
center line AX2 of the counterbore 42 and an axial center line AX1
of the nozzle hole 41 are coincide with each other. The diameter of
the nozzle hole 41 is smaller than that of the counterbore 42. The
nozzle hole 41 corresponds to a first hole and the counterbore 42
corresponds to a second hole.
[0028] The nozzle hole 41 has a constant diameter from a nozzle
hole inlet 411 to a nozzle hole outlet 412. The fuel can flow in
the nozzle hole 41 smoothly.
[0029] The fuel passed through the nozzle hole 41 is spread in the
counterbore 42 by its own pressure. The spread fuel is referred to
a fuel spray, hereinafter.
[0030] The fuel spray has a specified injection angle .theta.1 in
the counterbore 42. As shown in FIG. 3, the injection angle is
defined between the axial center line AX2 of the nozzle hole 41 and
an outer periphery line Se1 of the fuel spray. The injection angle
.theta.1 varies according to an injection pressure and an axial
length of the nozzle hole 41. As the injection angle .theta.1
becomes larger, the outer periphery line Se1 of the fuel spray
comes more close to an inner wall 422 of the counterbore 42. When
the fuel spray is most spread, the outer periphery line Se1 of the
fuel spray agrees with the inner wall 422 of the counterbore 42 at
a contact point 423.
[0031] A vertical distance "R" relative to the axial center line
AX1 is a minimum distance between an outer periphery 413 of the
nozzle hole outlet 412 and the contact point 423. An axial distance
"L" relative to the axial center line AX1 is a minimum distance
between the nozzle hole outlet 412 and the contact point 423. The
nozzle hole 41 and the counterbore 42 are formed in such a manner
as to satisfy a following formula:
R/(L.times.tan.theta.1)>6.0
[0032] Especially, regarding the fuel injector 1 for a diesel
engine, the fuel is pressurized to 25 Mpa-250 Mpa, whereby the
injection angle .theta.1 tends to become larger. According to the
present embodiment, even if the fuel is injected under the pressure
of 25 MPa-250 Mpa, the above formula is satisfied.
[0033] Referring to FIG. 3, an advantage and an operation of the
fuel injector 1 of the first embodiment will be explained,
hereinafter.
[0034] Generally, as the fuel injection pressure becomes higher, a
spreading force of the fuel spray becomes greater. Thus, the
injection angle .theta.1 also becomes larger. A distance between
the outer periphery line Se1 and the contact point 423 become
shorter.
[0035] When the distance between the outer periphery line Se1 and
the contact point 423 becomes short, the Coanda effect is generated
between the fuel spray and the inner wall 422 of the counterbore
42. The fuel spray is attracted toward the inner wall 422 due to
the Coanda effect. The shape of the fuel spray is changed. FIG. 3
shows an outer periphery line Se2 of the fuel spray. As a distance
between the outer periphery line Se1 and the contact point 423
becomes shorter, the Coanda effect is more generated. The fuel
spray is more attracted toward the contact point 423. Since the
diameter of the injection passage 4 is extremely small, the outer
periphery line Se1 is attracted to the contact point 423 due to the
Coanda effect.
[0036] The Coanda effect may cause following phenomena. The fuel
spray is attracted toward the inner wall 422 of the counterbore 42
and a part of the fuel spray remains in the counterbore 42. The
fuel spray is easily brought into contact with the inner wall 422
of the counterbore 42. The counterbore 42 has a space 421 through
which no fuel spray passes. A swirl of the fuel is generated in the
space 421. The swirl makes the remaining fuel spray flow out. When
the remaining fuel quantity becomes larger than the flowing-out
fuel quantity, a part of the fuel continues to remain in the space
421. The fuel may adhere to the injection passage 4, which is
referred to as a caulking. When the fuel spray is attracted toward
the inner wall 422 due to the Coanda effect, the shape of the fuel
spray will be changed. A penetration force and an infusibility of
the fuel spray changes in the combustion chamber.
[0037] In view of the above phenomena, the present inventors have
found out that specific dimensions of the injection passage 4 can
effectively restrict the Coanda effect. When the ratio R/L becomes
less than a specified value, the Coanda effect is generated. Thus,
according to the present embodiment, the ratio R/L is larger than
the specified value in order to restrict the Coanda effect. A
caulking in the injection passage 4 can be suppressed. An
instability of a fuel-spray shape can be suppressed.
[0038] FIGS. 4 and 5 are diagrams showing results of experiments
for explaining effects of the present embodiment. The experiments
are conducted with respect to fuel injectors "A" to "H" having the
injection passage 4 and the counterbore 42 respectively. The fuel
injection pressure Pr is varied from 25 Mpa to 250 Mpa. Regarding
each one of the fuel injectors "A" to "H", four experiments "Test1"
to "Test 4" are conducted. As shown in FIG. 5, each of the fuel
injectors "A" to "H" has its own distances "R" and "L". In each
experiment, the injection angle .theta. is measured to compute
"R/L.times.tan.theta.". The value of the "R/L.times.tan.theta." is
referred to as a characteristic value X, hereinafter. The
experiments "Test1" to "Test4" are conducted in this order. In the
experiment "Test1", the fuel injection pressure Pr is lowest among
the experiments. The fuel injection pressure Pr is increased along
with the order of experiments "Test1" to "Test4". That is, in the
experiment "Test4", the fuel injection pressure Pr is highest among
the experiments.
[0039] As the fuel injection pressure Pr is higher, the injection
angle .theta. becomes larger. However, the injection angle .theta.
in "Test3" is smaller than that in "Test2" with respect to the fuel
injectors "A", "B", "D", and "G". With respect to the fuel
injectors "A", "C" and "D", there is no caulking in each experiment
"Test1" to "Test4". On the other hand, with respect to the fuel
injectors "G" and "H", there is a caulking in each experiment
"Test1" to "Test4". With respect to the fuel injector "B", there is
no caulking in "Test3" and "Test4", however, there is a caulking in
"Test1" and "Test2". With respect to the fuel injectors "E" and
"F", there is no caulking in "Test1" and "Test2", however, there is
a caulking in "Test3".
[0040] Based on the experimental results shown in FIG. 4, a
correlation between the injection angle .theta. and the
characteristic value X is obtained. FIG. 5 shows an approximate
line Nr. When the characteristic value X is smaller than a
specified value, the injection angle .theta. becomes large. When
the characteristic value X is greater than the specified value, the
injection angle .theta. does not become large. It is considered
that the fuel spray is not attracted toward the inner wall 422 of
the counterbore 42 and the Coanda effect is restricted. According
to the experimental results, when the characteristic value X is
greater than or equal to a threshold "Th", the Coanda effect is
restricted. That is, when characteristic value X is greater than or
equal to 6.0, the Coanda effect is restricted, whereby the caulking
can be suppressed without making the injection angle .theta. large.
The injection angle .theta. is converged to a specified angle. The
shape of the fuel spray can be stabilized.
[0041] As above, the fuel injector is configured so that the
characteristic value X is greater than or equal to 6.0. The Coanda
effect can be suppressed. It can be avoided that the fuel adheres
to the inner wall 422 of a counterbore 42. The injection angle does
not vary significantly. Thus, a caulking in the injection passage
can be suppressed and an instability of a fuel-spray shape can be
suppressed.
[0042] According to the present embodiment, the fuel injector 1 has
the injection passage 4 which satisfies the above described
formula: R/(L.times.tan.theta.1)>6.0
[0043] Even if the fuel pressure is high, it is restricted that the
fuel spray is attracted to the inner wall 422 of the counterbore
42. A caulking can be suppressed effectively. The fuel spray shape
is stabilized and a combustion can be conducted effectively.
[0044] Furthermore, in the present embodiment, a plurality of
injection passages 4 is formed in the nozzle body 2. The
counterbore 42 of each injection passage 4 is formed so that the
injection passages 4 are not fluidly connected to each other. That
is, each injection passage 4 does not interfere with other
injection passages 4. Thereby, it can be suppressed that the
mechanical strength of the nozzle body 2 is decreased due to the
counterbores 42. Moreover, since each injection passage 4 does not
interfere with other injection passages 4, it can be suppressed
that the fuel spray collides with each other. The shape of the fuel
spray is not disturbed.
[0045] Furthermore, in the present embodiment, the diameter of the
nozzle hole inlet 411 is equal to the diameter of the nozzle hole
outlet 412. The flow velocity of the fuel in the injection passage
4 is increased. For this reason, the fuel flow in the injection
passage 4 may become a turbulent flow. However, according to the
present embodiment, since the inner diameter of the nozzle hole 41
is constant, the fuel flow in the nozzle hole 41 becomes the
laminar flow. The shape of the fuel spray can be stable.
[0046] The axial center line AX1 of the counterbore 42 and the
axial center line AX2 of the nozzle hole 41 are coincide with each
other. Thus, the counterbore 42 can be easily formed to satisfy the
above formula.
Second Embodiment
[0047] A second embodiment will be described hereinafter. In the
second embodiment, as shown in FIG. 6, the configuration of the
nozzle hole 43 is different from the first embodiment. FIG. 6 is a
schematic chart explaining the injection passage 4.
[0048] An inner diameter of the nozzle hole inlet 411 is greater
than that of the nozzle hole outlet 412. The inner diameter of the
nozzle hole 43 is gradually decreased from the nozzle hole inlet
411 toward the nozzle hole outlet 412. The vertical distance "R",
the axial distance "L", the injection angle .theta.2 are defined as
to satisfy the following formula: R/(L.times.tan.theta.2)>6.
[0049] A caulking in the injection passage 4 can be suppressed. An
instability of a fuel-spray shape can be suppressed.
[0050] Moreover, since the inner diameter of the nozzle hole 43 is
gradually decreased from the nozzle hole inlet 411 toward the
nozzle hole outlet 412, the flow velocity of the fuel is increased
in the injection passage 4. Thereby, the penetration force of the
fuel spray is increased.
Third Embodiment
[0051] A third embodiment will be described hereinafter. In the
third embodiment, as shown in FIG. 7, the configuration of the
counterbore 44 is different from the first embodiment. FIG. 7 is a
schematic chart explaining the injection passage 4.
[0052] An axial center line AX2 of the counterbore 44 deviates from
an axial center line AX1 of the nozzle hole 44. Since the center
line of the fuel spray deviates from the center line of the
counterbore 44, the outer diameter of the fuel spray is different
from the inner diameter of the counterbore 44. The contact point
423 exists on the inner wall 422 of a counterbore 44. A caulking in
the injection passage 4 can be suppressed and an instability of a
fuel-spray shape can be suppressed.
Other Embodiments
[0053] The present disclosure should not be limited to the above
embodiments, but may be implemented in other ways without departing
from the spirit of the disclosure. FIGS. 8 and 9 are schematic
charts explaining the injection passage 4.
[0054] FIG. 8 shows a first modification in which the inner
diameter of the inner wall 422 gradually increases toward the
outlet of the injection passage 4. The injection passage 4 is
configures to satisfy the formula:
R/(L.times.tan.theta.4)>6.0
[0055] FIG. 9 shows a second modification in which the injection
passage 4 has three counterbores 142, 242, 342 of which inner
diameter is different from each other. The contact point 423 exists
between a first counterbore 142 and the second counterbore 242.
[0056] The first counterbore 142 is configured to satisfy the
following formula: R/(L.times.tan.theta.5)>6.0
[0057] Furthermore, according to a third modification, any one of
the nozzle hole 41 and the counterbore 42 may be an ellipse.
* * * * *